From No. EP-A-44 428 it is known to produce by comminuting, thermal digestion and saccharification of starch-containing raw materials a mash for producing alcohol from starch or starch-containing raw materials. There is known a number of sugar containing raw materials from which can directly be obtained sugar solutions by extraction, and it is known to degrade such sugar solutions down to glucose and to subject a mash obtained in this manner to fermentation. The fermentation process requires different conditions, depending on the composition of the raw materials and of the mash, and it requires a relatively long reaction time for completion. It is a drawback of known fermentation processes that the mashes and fermentable substrates contain the fermentable sugar as well as the fermentation products in concentrations changing during the fermentation, which adversely influence the reaction speed or fermentation speed.